Phosphorus‐containing benzoxazine modified epoxy resin: High flame retardancy, low dielectric, and low water absorption

Abstract A phosphorous‐containing benzoxazine, (3‐(4‐hydroxyphenyl)‐3,4‐dihydro‐2H‐benzo[e][1,3]oxazin‐4‐yl)diphenylphosphine oxide (DPOBH), was synthesized and used as flame retardant and co‐curing agent in the presence of 4,4′‐diaminodiphenylsulfone (DDS) for diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin. The flame retardancy, thermal stability, T g , dielectric properties, and water absorption properties of epoxy resins (EP) were investigated and compared. The incorporation of DPOBH results in ca. 40%–45% increase of limiting oxygen index (LOI) values. UL‐94 V‐0 rating could be achieved for EP/DPOBH 1.2 sample with the LOI value of 35.1%. Compared with EP, ca. 47% decrease of peak heat release rate (PHRR) could be obtained for EP/DPOBH 1.2 . According to the results of cone calorimetry tests (CCT), DPOBH could play roles in both gas and condensed phases. Moreover, the incorporation of DPOBH could reduce the water absorption rate, dielectric constant, and dielectric loss. All results suggest that DPOBH is a type of flame retardant suitable for EP used in electronic fields.